Association of Escherichia coli O157:H7 density change with hydrogen peroxide but not carbohydrate concentration in the leaf content of different lettuce types and spinach

Authors: Brandl, Maria; Hua, Sui Sheng; Sarreal, Siov Bouy

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2025
Publication Date: 2/19/2025
Citation: Brandl, M., Hua, S.T., Sarreal, S.L. 2025. Association of Escherichia coli O157:H7 density change with hydrogen peroxide but not carbohydrate concentration in the leaf content of different lettuce types and spinach. Foods. 14(4):709. https://doi.org/10.3390/foods14040709.
DOI: https://doi.org/10.3390/foods14040709

Interpretive Summary: Lettuce leaf injury commonly occurs from farm through table and causes leakage of cellular contents that may affect foodborne pathogen colonization. Shiga toxin-producing E. coli has been recovered from crops and has caused outbreaks of foodborne illness associated with lettuce in several countries. The effect of cellular content from young and middle leaves of different lettuce types, and those of spinach, on the multiplication of E. coli O157:H7 (EcO157) was investigated to identify chemical traits involved in colonization by this pathogen. Lettuce types consisted of romaine, iceberg, butterhead, and green and red leaf. Lysates of various lettuce types and leaf ages promoted different E. coli O157:H7 growth. Baby spinach lysates promoted greater E. coli multiplication than lettuce lysates. Young leaf lysates had lower H2O2 concentrations than middle leaf lysates. E. coli multiplication in the lysates negatively related to their H2O2 concentration. No relation was observed between E. coli growth in the lysates and sugar concentration. Given the known opportunistic colonization of compromised leaf tissue by this pathogen, as well as the increasing consumption of leafy vegetables as fresh-cut product and as homogenized health beverages, these phenotypes provide important information in the breeding of lettuce genotypes to improve public health.

Technical Abstract: Lettuce leaf injury commonly occurs from farm through table and causes leakage of cellular contents that may affect foodborne pathogen colonization. Shiga toxin-producing E. coli has been recovered from crops and has caused outbreaks of foodborne illness associated with lettuce in several countries. The effect of cellular content from young and middle leaves of different lettuce types on the multiplication of E. coli O157:H7 (EcO157) was investigated to identify chemical traits involved in colonization by this pathogen. Lettuce types consisted of romaine, iceberg, butterhead, and green and red leaf. EcO157 was inoculated into filtered lettuce lysates immediately after leaf homogenization and densities were monitored over five hours. Concentration of fructose, glucose and sucrose in the lysates was measured by HPLC and that of H2O2 was quantified with the Amplex Red assay. The young leaves of iceberg, romaine and green leaf lettuce held significantly greater total amounts of the three carbohydrates, while butterhead middle leaves contained the least. Except for iceberg, middle leaves generally contained significantly greater H2O2 concentrations than young leaves within each lettuce type (P < 0.05). The extent of EcO157 multiplication in the lysates related neither to the individual nor total concentration of the three carbohydrates but, was significantly negatively related to H2O2 concentration (R2 = 0.555; P = 0.014). In support of this relationship, lysates of bagged baby spinach were among the lowest in H2O2 levels and promoted the highest EcO157 multiplication; and supplementation of romaine middle leaf lysates with superoxide dismutase and catalase significantly enhanced EcO157 multiplication. Given the known opportunistic colonization of compromised lettuce leaf tissue by this pathogen, as well as the increasing consumption of leafy vegetables as fresh-cut product and in homogenized health beverages, these phenotypes provide important information in the breeding of lettuce genotypes to improve public health.